If you have installed the below hacked version, you must delete it, and reboot then install the official.

To delete it either open iFile and browse to
/private/var/stash/Applications/ and then delete Netflix.app or use SSH the same way you copied it, but instead delete it.

Then reboot and go to the app store and install the official one

For history sakes I will reduce and recolor the previous method of installing Netflix

After a quick google search I found this article which had step by step instructions for using Netflix on a 3g[s] but it does not work on the now jailbroke iPhone4 *because of the UserAgent strings I assume*

So after some quick thinking, I found a way to do it...here is my copy/paste/change method of doing so. Thanks to the original writer at TMCNet....here we go...

3) In iTunes, right-click the Netflix for iPad application & click 'Show in Windows Explorer' or 'Show in Finder'

4) Rename Netflix 1.0.4.ipa to Netflix 1.0.4.zip.

5) Extract the entire ZIP file somewhere.

6) Go into the extracted folder, then the Payload folder.There you'll see the Netflix.app folder containing the entire app.

7) Copy Netflix.app folder to your iPhone using SSH. After you SSH into your phone (I use Cyberduck on Mac), navigate to:
/private/var/stash/Applications/, which is where the Netflix.app goes.

8) Change permissions on the Netflix.app folder to 755 using this command: (On mac using Cyberduck click on 'Go - Open in Terminal App' then login
chmod -R 755 Netflix.app

Note: If you use the Terminal app on the iPhone to change permissions, make sure to run "su root" or else you will get this error: "Terminal problem. (operation not permitted)"

9) Respring (or restart) your phone.

10) In the App Store buy Perfect Browser for $1.99. When it is installed open it and click the wrenches for settings then click on Desktop Rendering then choose Safari iPad and click the Green Check Mark to accept the changes.

I followed the guide to a T and when I load up the movie in Perfect Browser it just closes and sits on my homescreen, quicktime never loads. I read over the guide again and everything was done right. I have no idea as to why the movie never loads.

EDIT- Seems to be the phone needed an extra respring after downloading Perfect Browser. All is well now, can't wait to abuse this, thanks.